Unimolecular decomposition pathways of negatively charged nitriles by ab initio molecular dynamics

Abstract

We present negative ion-mode simulations within the QCEIMS program [Grimme, Angew. Chem., Int. Ed., 2013, 52, 6306]. It is an exhaustive and robust ab initio molecular dynamics/stochastic algorithm used to perform simulations of unimolecular decomposition of anions, in unprecedented detail. The objective of this approach is to compliment electron attachment spectroscopy and aid in the interpretation of relevant dissociation dynamics. Prototypical simulations are performed for the four nitrile compounds acetonitrile, cyanamide, aminoacetonitrile, and trifluoroacetonitrile. The unique decomposition pathways which naturally occur in the simulations are addressed along with fractional yields, reaction times and relative intensities of the fragments. Furthermore, trajectories of selected decomposition pathways of the aminoacetonitrile anion are investigated in greater detail, where we find that the relevant HOMO of the anion has a mixed π* and σ* character delocalized over the entire molecule.

Quantum chemical calculation of electron ionization mass spectra for general organic and inorganic molecules

“…, determinative peak-series. In the analysis of the production run trajectories, we use the same script as previously reported 12 to identify fractional yields and distinguish between structural isomers that contribute to the same peak, or mass-to-charge ratio m / z . The comparison of the experimental and computed MS, for all molecules, is visualized in Fig.…”

“…, in electron ionization (EI) mass spectrometry, 2 , 3 collision induced dissociation (CID), 4 – 6 surface induced dissociation, 7 – 9 and dissociative electron attachment (DEA). 10 – 12 AIMD simulations provide a promising alternative to the well-established statistical theories ( e.g. , Eyring's quasi-equilibrium theory, 13 and Rice–Ramsperger–Kassel–Marcus (RRKM) theory 14 – 17 ).…”

“…In the most recent study, QCEIMS was extended to successfully predict the unimolecular decomposition pathways of four negatively charged nitrile compounds upon low energy electron attachment. 12 …”

Software Tools and Approaches for Compound Identification of LC-MS/MS Data in Metabolomics

“…Quantum chemistry methods use first-principles and purely physical and chemical information to generate mass spectra. In a major breakthrough for computational mass spectrometry, Grimme described in 2013 how Born–Oppenheimer ab initio molecular dynamics can be used to generate in silico electron ionization mass spectra of any given compound [ 65 , 66 , 67 , 68 , 69 ]. An overview of methods for in silico generation of mass spectra, including commercially or freely available algorithms is listed in Table 4 .…”

On-the-fly dynamics simulations of transient anions

“…If the system of interest is a large molecule, one has to restrict the multidimensional potential energy surfaces to one 21 or two 17 vibrational coordinates. Molecular dynamics simulations are sometimes employed for the later stages of DEA, [22][23][24] but without accounting for the autodetachment probability of its initial stage, when the anion is still transient. Alternatively, potential energy curves computed along reaction coordinates can also help understanding DEA mechanisms.…”